Thank you all for the advice you have given me so far in caring for my rescue fish (esp. necromancer and marcus, yall are great). Can someone help me with figuring out why my filters keep getting moldy? Its white and all over the filter that youre not supposed to throw away, the aquarium lid, and the lid of the filtration unit. Thanks!

mold develops in those area because of the moisture
and the presence of bacteria. wipe it with rags soak
in disinfectant and it will be gone.

when you say over the filter that you don't throw away do you mean inside the filter on the media or outside around the filter?? if it outside around the filter check for damp, wipe out and give plenty of time with door open to dry. in lid have you got a condensation cover? ie a glass inside the main cover. these help but may not completely remove it. I had a small amount myself where the filter was splashing back onto the wood. as soon as I noticed I left the lid open for a few days to dry it and it went. The only problem with mold is it returns easy as soon as damp comes back. silica( not sure that's spelt right?) the little bags that absorb moister can help too. you can get larger bag too. one other thought, was the tank used as a salt water tank? it may be salt build up? this turns white too.

Thanks for your replies. The mold is growing right at the top of the water line of the filter bucket and where the filter dips into the water. Concerning the lid, I think you may both be right. When I first got the fish, I was told that the tank used to be a salt water tank. Also, I have a habit of leaving the lid off the filter area, so I will try these suggestions and post the results. Thanks again- yall are awesome.

There is a filmy substance building up on the rocks in my tank even though I am doing my water changes like you instructed. It started after I got some feeder minnows from a really suspect redneck bait store. Is it time to throw these rocks away????? I have been having issues with my fish ever since those minnows hit the tank, and I cant quite get my tank back right. And im pissed about it, mainly because I remember what yall told me about watching what I feed my Oscar- and I gave him these minnows against the suspicions in my head about the cleanliness of the place I got them from.

I doubt whether the introduction of fish have anything to do with what is on the rocks. If you're worried, take the rocks out and give them a good wash, no need to throw them away. Just remember that a tank is a living environment. Fish are not the only live creatures in your tank, there will be invisible life that you cannot see. Algae comes in many forms and guises, it could be a form of algae that is on your rocks.

If you're worried about your tank, carry out some water tests, ammonia, nitrates, nitrite and pH, this will give you an indication if you've got serious problems.

If you must feed to your Oscars live fish, get them from a reputable dealer, but I think you realise that.

Thanks for your response. I will do this today. When I first got the Ocsar, I gave him the live fish only as a treat per the book I got for his care, but recently I have been doing it to keep him alive (i think..), because he will not eat the pellets anymore. They just sink to the bottom and get moldy and gross before I scoop them out.